Contamination and residuals (C&R) detection is an integral part of the manufacture of semiconductor components. Typical contaminants found in the manufacturing process are impurities present in the liquid used to dissolve photoresist layers. A typical residual is a portion of photoresist, which is commonly polymethylmethacrylate (PMMA). As the size of the components decreases and their complexity grows, the effect of a specific contaminant on the component becomes more acute, and the detection of contaminants and also of residual chemicals becomes more important. In Rapid Thermal Processing, edited by Richard Fair, Academic Press, Inc., which is incorporated herein by reference, the author gives an example of a "killer" defect size in semiconductor processing for a gate thickness of 7 nm, wherein a defect sized 3.5 nm could be fatal. Typically, a rule of thumb for a killer defect size is that the defect is of the order of half the size of the design rule used.
Although both wet and dry cleaning processes are used in the manufacture of semiconductor components, neither is completely effective in removing contaminants, such as residues of photoresist, from the surface of the wafer. Typically this is compensated for by cleaning the wafer by about 30% more than the optimal cleaning time, entailing extra cost, time and increased possibility of damaging the components on the wafer.
There are many processes known in the art for C&R detection. In high-speed optical defect review systems, which are typically integrated into a production line for components, the cost of inspection is relatively high. In addition, for some layers such systems only allow low sampling rates, and do not detect non-visible residuals for any layers.
An alternative system for C&R detection is optical spectral analysis, wherein photons from pre-ionized contaminants are detected, usually by a CCD array detector. However, in order to evaluate if the photons are from a contaminant, the optical spectral analysis system has to analyze the wavelength of the received photons.
While any C&R detection process is operating, it must be absolutely non-destructive to components being checked.